Simplify the Tense
Unless you’re a time traveller (and therefore comfortable with temporal paradoxes), the best rule of thumb is to stick to the present tense as much as possible and make occasional forays to other tenses as needed.
English has twelve tenses. Present tense is the only real tense—all the others are factors of our imagination, so don’t make time travellers of your readers by hiking around through your imaginary temporal landscapes.
